The Phenomenon Map: Which Architectures Show It
Ongoing research. This is an experimental result from active work, not a settled conclusion. The numbers are what we measured and the method is described so you can judge it, but the programme is still running and later experiments may revise what it means. More about this programme.
EXPLORATORY. Not a preregistered study. Local CPU, 105 training runs, no GPU, no cost.
Program v2 tier 3, item E3, which subsumes A1. Decisive computation: . Output: analysis/phenomenon_map.py. Reproduce with analysis/phenomenon_map.jsonpython analysis/phenomenon_map.py in about forty minutes on a throttled laptop CPU.
The question
Every positive result in this project is a GRU result on one task. The confirmed expansion, D6's measurement-frame finding, D8's optimizer scoping, F2's leading indicator and F3's feature-creation result all sit in that single cell. E3 asks whether any of it is a fact about recurrence or a fact about the GRU.
A1's design requirement is the crux. The transformer's weak expansion in the original confirmation was confounded: copying a token from lag positions back is attention's native operation, so a transformer never has to build a mechanism for delayed-copy, and an absent signal proves nothing. A fair test needs a task attention cannot solve with one lookup. The E1-accepted dispatch-copy tasks supply it.
Learning rates are screened per cell on seed 997, excluded from the four measurement seeds, because comparing architectures at a shared rate confounds "lacks the phenomenon" with "was mistuned".
The grid
Width 48, 900 steps, four seeds. sharp is F3's sharpness endpoint: steps to cross from a quarter to three quarters of the run's own accuracy range. rise is rank-8 residual energy above baseline, against the preregistered 0.05 materiality floor.
| Architecture | Task | lr | Learned | Final | Sharp | Rise | Clears floor |
|---|---|---|---|---|---|---|---|
| gru | delayed-copy | 0.012 | 4/4 | 0.9809 | 82 | +0.2184 | yes |
| lstm | delayed-copy | 0.012 | 4/4 | 0.9980 | 72 | +0.2279 | yes |
| rnn | delayed-copy | 0.012 | 4/4 | 1.0000 | 28 | +0.0498 | no |
| gru-2layer | delayed-copy | 0.012 | 4/4 | 0.9940 | 50 | +0.2659 | yes |
| transformer | delayed-copy | 0.012 | 4/4 | 1.0000 | 5 | +0.0383 | no |
| gru | dispatch-copy-8lag | 0.005 | 4/4 | 0.5590 | 299 | +0.2351 | yes |
| lstm | dispatch-copy-8lag | 0.002 | 4/4 | 0.4977 | 371 | +0.2571 | yes |
| rnn | dispatch-copy-8lag | 0.002 | 0/4 | 0.2253 | , | , | , |
| gru-2layer | dispatch-copy-8lag | 0.005 | 4/4 | 0.7100 | 282 | +0.3638 | yes |
| transformer | dispatch-copy-8lag | 0.002 | 0/4 | 0.2503 | , | , | , |
| gru | dispatch-copy-wide-vocab | 0.012 | 4/4 | 0.6240 | 285 | +0.1747 | yes |
| lstm | dispatch-copy-wide-vocab | 0.005 | 4/4 | 0.7063 | 366 | +0.2053 | yes |
| rnn | dispatch-copy-wide-vocab | 0.005 | 0/4 | 0.2637 | , | , | , |
| gru-2layer | dispatch-copy-wide-vocab | 0.012 | 4/4 | 0.7558 | 258 | +0.3286 | yes |
| transformer | dispatch-copy-wide-vocab | 0.005 | 4/4 | 0.6025 | 531 | +0.0313 | no |
Result 1: the phenomenon is not GRU-specific
The LSTM shows it at full magnitude on every task it learns: +0.2279, +0.2571, +0.2053, against the GRU reference of +0.2184. The two-layer GRU shows it more strongly still (+0.2659, +0.3638, +0.3286).
A1 is answered. Nine of nine gated-recurrent cells clear the materiality floor, on all three tasks. Everything built on the expansion is no longer scoped to one architecture.
Result 2: it is a gated recurrence phenomenon, and the transformer cell proves it
Zero of three measured non-gated cells clear the floor. That includes the case A1 was designed around, and it is the most important row in the table.
On dispatch-copy-wide-vocab, the transformer:
- does learn the task (
0.6025, comparable to the GRU's0.6240); - has the slowest transition in the entire grid (
531steps, against the GRU's285); - and still shows no expansion (
+0.0313, below the floor).
That closes the confound. The transformer's absent signal on delayed-copy could be dismissed as "the task was free for attention", sharpness 5 says it solved the task almost instantly. On wide-vocab there is no such excuse: attention has to work for hundreds of steps and produces no expansion while doing it.
And it is not about how slow the transition is
The obvious alternative explanation is that the expansion tracks transition duration: more representational work, more reorganisation. The grid refuses it.
The transformer on dispatch-copy-wide-vocab has the longest transition measured (531 steps) and the smallest rise (+0.0313). The two-layer GRU on the same task transitions in half the time (258) with ten times the rise (+0.3286).
Duration does not predict the expansion. Architecture does.
Result 3: the vanilla RNN is not a clean test either way
The ungated cell fails to learn both dispatch tasks (0 of 4 in each), and on delayed-copy it solves the task almost immediately (final 1.0000, sharpness 28) with a rise below the floor. So its non-clearing is confounded in the same way the transformer's originally was.
Recorded as untested rather than negative. An ungated recurrent cell either finds the task trivial or cannot do it at all at this scale, and neither case measures what E3 is asking.
The map
| Family | Expansion | Evidence |
|---|---|---|
| Gated recurrence (GRU, LSTM, 2-layer GRU) | present, at full magnitude | 9 of 9 measured cells clear the floor, across three tasks |
| Attention (transformer) | absent | 0 of 2 measured cells, including one with the grid's slowest transition |
| Ungated recurrence (vanilla RNN) | untested | Solves the easy task instantly, cannot learn the hard ones |
What this changes for the program
- Every downstream result gains scope. D6, D8, F2 and F3 were GRU-only findings. They are now findings about gated recurrence, pending direct replication of each in an LSTM, which is now cheap and should be the next thing run.
- F2's leading indicator is worth re-testing in the LSTM. It is the one result with practical use, and it now has a second architecture to be checked in.
- The gating mechanism becomes the object of study. The dividing line in this grid is not depth, not recurrence, and not transition duration: it is whether the cell has multiplicative gates. Why a gate produces a representational expansion at the moment of learning is a question this project has not asked and can now afford to.
Limits
- One width (48), one step budget (900), one optimizer (AdamW), four seeds per cell.
- Learning rates screened over three values. A cell that failed to learn might succeed at a rate outside that range; the two 0-of-4 rows should be read as "did not learn here".
- The transformer is one configuration (1 layer, 4 heads, feedforward 96). Depth and head count are not varied, and a deeper transformer is a different object.
dispatch-copyis one task family in two configurations. The grid has three tasks but two generators, so "across tasks" is weaker than it looks.